Abstract:

Effective sustained release of microbial pesticides in aquatic
environments can be achieved by the combination of buoyant particles with
a particulate microbial active ingredient. The resulting materials in the
form of a particulate have combined density of less than one. The
materials are then dispersed into gypsum slurry that is poured into
briquette molds, or made into granules or pellets of various sizes, to
form a solid, sinking, pest control composition. Once applied in aquatic
field sites, the surface of the matrix slowly dissolves, releasing many
minute buoyant pesticide laden particles to the water surface over the
life of the product. Once at the surface, the particulate microbial
pesticide(s) release from the buoyant particles and are distributed
throughout the water column to be ingested by susceptible immature filter
feeding mosquitoes and pestiferous flies.

Claims:

1-13. (canceled)

14. A solid pest control unit comprising an effective amount of a
particulate microbial pest control agent, an effective slow release
amount of a plaster having a high compressive strength of at least 500
lbs. per square inch, and a hardening amount of water, wherein the unit
is sufficiently hard to be distributed over large areas by mechanical
means, has a surface area of about 10 to about 50,000 mm2, when
immersed in an aqueous pest breeding site can provide an effective amount
of the pest control agent, and when dry does not release the agent.

15. The solid pest control unit of claim 14 wherein the surface area of
the object is about 2,000 to 30,000 mm.sup.2.

16. The solid pest control unit of claim 15 wherein the surface area of
the object is about 2,500 to 7,500 mm.sup.2.

17. The pest control unit of claim 14 wherein the solid pest control means
has a regular shape.

18. The pest control unit of claim 17 wherein the regular shape is a
briquette, a pillow, a sphere, a prism, or a pyramid.

19. A pest control unit of claim 17 wherein the regular shape is a
cylinder having dimensions of about 1 to 100 millimeters in diameter and
about 1 to 100 millimeters in height.

20. The pest control unit of claim 17 wherein the regular shape is a
truncated cone having dimensions of about 20 to 45 millimeters on the
major diameter, about 15 to 35 millimeters on the minor diameter, and
about 15 to 40 millimeters in height.

21. The pest control unit of claim 19 wherein the dimensions of the
truncated cone are about 35 to 40 millimeters in the major diameter,
about 30 to 35 millimeters in the minor diameter, and about 30 to 35
millimeters in height.

22. The solid pest control unit of claim 21 wherein the surface area of
the solid pest control unit is about 4,000 to 7,000 mm2 and wherein
the mass of the solid pest control means is about 0.2 to 100 grams.

23. The solid pest control unit of claim 21 wherein the surface area of
the solid pest control unit is about 4,000 to 7,000 mm2 and wherein
the mass of the solid pest control means is about 3 to 45 grams.

24-25. (canceled)

Description:

FIELD OF THE INVENTION

[0001]The invention relates to a microbial pesticidal sustained release
composition, treatment unit and means for the control of pestiferous
insects. The treatment unit can be distributed in aquatic environments to
provide long lasting effective pest control. The unit contacts water at
the surface and sinks to the bottom of the aquatic environment. When in
contact with water, the pest control unit and means releases pesticide
materials after sinking, providing desired low level pesticide
concentrations, to achieve effective pest control over prolonged time
periods.

BACKGROUND OF THE INVENTION

[0002]Mosquitoes and biting flies develop worldwide in aquatic
environments during temperate months, creating serious public health
problems through disease transmission and biting insect annoyance.
Control of these public health insects is costly due to the significant
labor, equipment and material requirement necessary. To achieve control,
all potential breeding sites within the pest insect's flight range must
be inspected weekly during summer months, and if found breeding, control
materials must be applied. The development of effective, soluble
pesticide controlled release formulations for aquatic environments
lasting up to 150 days in the early 1980's by Sjogren (U.S. Pat. No.
4,732,762) provided significant labor savings and reduced control costs.
This technology has been commercialized using the soluble insect growth
regulator S-Methoprene, and has gained widespread acceptance and use.

[0003]In the mid 1980's, a microbial pathogen Bacillus thuringiensis
israelensis (Bti) was discovered and subsequently commercialized for pest
control. In the mid 1990's, a second microbial pathogen of mosquitoes,
Bacillus sphericus (Bsph) was also brought to market. These microbial
pesticides are highly selective for small immature biting flies
(Nematocera), are recognized for their environmental compatibility, and
have become control materials of choice for use in mosquito control
programs. To be effective these microbial pathogen particles (>1.0
specific gravity) must be applied to the water surface and ingested by
aquatic immature biting fly stages, before they settle out of the water
column. This is now achieved for short term control by liquid or floating
corn cob granules (<1/2 mesh) applied to flooded field sites that
contain mosquito larvae. The duration of control achieved by such liquid
or granular treatments vary with the dosage applied, ranging from 24 to
72 hours with Bti, and 7 to 28 days with Bsph.

[0004]In 1996, Sjogren (U.S. Pat. No. 5,484,600) described a timed-release
microbial granule formulation in the form of a composite particle. The
particle is in the form of a dense core, a flotation particle, a
pesticide and an adhesive that delivered microbial pesticidal particles
to the water surface for mosquito control. In that invention, microbial
powders were blended with a buoyant agent and attached to the outside of
a sinking granular carrier. A slow dissolving, water soluble protein
binder released the buoyant agent and microbial pesticide to the water
surface over 10 to 30 days.

[0005]Kase (U.S. Pat. No. 4,631,857) describes the delivery of particulate
(1.5 to 15 micron) microbial pesticide consisting of a mixture of cork, a
larvicidal micro-organism (Bti), gypsum plaster and water sufficient to
set the plaster to produce a floating molded unit. When applied into
small aquatic field sites, the plaster slowly dissolves releasing the Bti
at the water surface. Although the composition is reported to control
mosquitoes for up to one month in very small field sites, the invention
has a number of disadvantages that are overcome by the present invention.
They are: 1) the floating molded unit releases Bti directly into the
water as the plaster disintegrates, which limits the lateral dispersal of
the sinking particulate pesticide; 2) the floating unit can be beached by
winds rendering it ineffective, and anchoring it in place is labor
intensive; 3) the unit's relatively large size, about 2 inches diameter,
and its light weight, renders it impractical to disperse with mechanical
equipment; and 4) its control effectiveness is limited to approximately
30 days.

[0006]Particulate pest control compositions used in water perform best
when they are evenly distributed in field mosquito breeding sites, and
remain in place after application, delivering particulate pathogenic
particles at the water surface in their vicinity. Floating compositions
readily drift away from where they are applied, and do not achieve the
uniform distribution of microbial particles at the water surface in large
sites, required for pest insect feeding ingestion. Thus, sinking
compositions perform more dependably than floating compositions under
diverse field conditions.

[0007]The development of an effective sinking sustained release microbial
composition which delivers particulate, non-water soluble, microbial
pesticides at the water surface over a prolonged period to control
aquatic biting flies, is difficult to achieve. For microbial particulate
pesticides to be effective they must be uniformly distributed on the
water surface of field sites and remain available long enough to be
ingested by filter feeding mosquito larvae. Granule and pellet
compositions must be small enough in size to permit large numbers to be
distributed with mechanical equipment to provide multiple release loci.
For such small units to be effective, the composition must be highly
efficient to continuously deliver pest controlling quantities of
particulate pesticides.

[0008]Accordingly, a substantial need exists for a sinking sustained
controlled release microbial pesticide composition that remain in place
when applied, achieve effective microbial control of pest populations,
that provides a continuous release of microbial pesticide to the water
surface to maintains an effective mosquito controlling concentration for
long periods during the temperate or breeding season.

BRIEF DISCUSSION OF THE INVENTION

[0009]I have found a composition comprised of a microbial pesticide and a
matrix is an efficient long term (>30 days) means of achieving
mosquito control when applied uniformly to field mosquito breeding sites.
Such a matrix can include a buoyant agent, aqueous slurry of microbial
pesticide and means to form a matrix. The pesticide slurry can be loaded
onto the buoyant agent to produce a microbial pesticide component. Such
loaded buoyant particles have a specific gravity of <1.0, after which
the resulting particles are dried and reduced in size back to discrete
particles by grinding, can be blended with a plaster or gypsum cement
slurry and cast into molds to set. The molded unit is an efficient
long-term means of achieving mosquito control when applied uniformly to
field mosquito breeding sites.

[0010]No water-soluble adhesives are used. A gypsum briquette is used as
the controlled release mechanism, into which buoyant particles are loaded
with microbial insecticide and incorporated to form a heaver than water
briquette invention that can easily be tossed into water bodies at
regular intervals, or applied in pellet form by hand or mechanical means.
Upon application, such articles effectively penetrate vegetation
canopies, sink to the bottom of water bodies and stay in place over time,
slowly and continually releasing very large numbers of individually
loaded microbial insecticide particles to the water surface with the
consistency and uniformity necessary to provide dependable control.

[0011]The present invention overcomes the limitations of floating
compositions by use of a sinking composition that: 1) remains in place at
the bottom of an aquatic environment, when applied in field sites, thus
providing uniformly spaced release loci; 2) slowly releases many buoyant
(<1.0 specific gravity) particles each loaded with particulate
microbial pesticide, each of which transports the microbial particles to
the water surface. Once pesticidal laden particles release to the surface
they disperse throughout the site, aggregating and slowly releasing their
payload in protected areas where target larval insect stages aggregate
and feed; 3) can be made into a) pellets and/or granules that can be
mechanically distributed in the environment, and b) briquettes of various
sizes for hand application to field sites on equidistant intervals. Field
trials have demonstrated the present invention controls for >60 days
with pellets (Mulla, 2003) and >150 days with briquettes as small as
12 grams (Su, 2003). The pest control agent comprises a microbial agent
comprising one or more of a bacterium, a fungus, a virus, or a
combination or mixture thereof. The particulate pest control agent
comprises an insecticide which is present in the total composition at an
amount of about 20 wt-% or less. The microbial insecticide can be a
mosquito control agent and can use Bacillus thuringiensis israelensis
alone, Bacillus sphericus alone, both Bacillus thuringiensis israelensis
and Bacillus sphericus microbial control agents in combination.
Genetically modified forms and or combinations of these strains can be
used. The unit of the invention can be made up in a plaster composition.
A preferred plaster has a high compressive strength that ranges from
about 2,000 to about 15,000 pounds per square inch or from about 4,000 to
14,000 pounds per square inch. The pest control agent can be present in
the total composition in an amount of about 2 to about 15 wt-percent and
the plaster in an amount about 30 to 90 wt-%. The term particulate or
particle means a small unit of millimeter size ranging up to a larger
unit of substantial mass that can be mechanically or manually
distributed.

[0012]In the case of Bti products, the typical bioassay does not measure
the concentration of anything in particular, but rather evaluates overall
potency, or killing power against the intended target. The Basic
Insecticide Bioassay, by dosing the insects, avoids most of the factors
such as formulation, application method, organic matter, and palatability
that might influence how much toxicant gets to the insect. With most
toxicants, there is a regular relationship between the toxicant dose and
the percentage of insects that are affected. The characteristics of the
relationship for any given toxicant and insect species can be learned by
dosing groups of the insects with different amounts of the toxicant to
develop a dose-response curve. All doses (or more properly,
concentrations) below 0.4 mg/ml killed no larvae. All concentrations
above 1.4 mg/ml killed all of the larvae. In between these two
concentrations, along the response curve, are concentrations that will
kill some fraction of the test insects. Approximately 0.77 mg/ml will
typically kill about one half an insect population. Every Bti bioassay
must include the simultaneous bioassay of a reference standard against
the same group of test insects. A reference standard is a preparation of
the same type of Bti with an established potency.

BRIEF DISCUSSION OF THE FIGURES

[0013]FIGS. 1-5 show the efficacy of the pesticide invention in preventing
emergence of certain mosquitoes over a lengthy treatment.

[0014]FIG. 6 shows the residual amount of briquette embodiment of the
invention in the flooded site over time.

[0015]FIG. 7 shows the water temperature of the test aqueous location.

DETAILED DISCUSSION OF THE INVENTION

[0016]The pest control unit of the invention typically is in the form of a
solid regular or irregular shape that can be distributed into the
environment. The material must be mechanically stable such that the
forces of production, bagging, storage, transportation and distribution
into the environment does not substantially reduce the unit or particle
size or change the geometry of the unit. The unit can have virtually any
regular or irregular shape. The unit can have an irregular or
agglomerated shape with no significant symmetry and have a irregular
surface and structure. A preferred form of the unit of the invention is a
regular geometric shape. Such shapes include a variety of well known
geometric shapes including briquette, a pillow, a sphere, a generic
prism, a pyramid, oval, cylinder, truncated cylinder, cube, rectangular
prism, triangular prism and others. The shapes can have a surface area
that ranges from about 10 to about 50,000 mm2, preferably about
2,000 to 30,000 mm2 and often 2,500 to about 7,500 mm2. The
major dimension of such a unit ranges from about 1 millimeter size up to
as large as 10 cm in major dimension. The unit can be shaped to permit
easy grip and throw if distributed individually. The solid pest control
unit comprising an effective amount of a particulate microbial pest
control agent can use an effective slow release amount of a plaster
having a high compressive strength of at least 500 lbs. per square inch,
and a hardening amount of water. The unit is sufficiently hard to be
distributed over large areas by mechanical means. The unit has a surface
area of about 10 to about 50,000 mm2, when immersed in an aqueous
pest breeding site can provide an effective amount of the pest control
agent, and when dry does not release the agent. The unit can be a
cylinder having dimensions of about 1 to 100 millimeters in diameter and
about 1 to 100 millimeters in height. The unit can have a regular shape
is as a truncated cone having dimensions of about 20 to 45 millimeters on
the major diameter, about 15 to 35 millimeters on the minor diameter, and
about 15 to 40 millimeters in height. The truncated cone is about 35 to
40 millimeters in the major diameter, about 30 to 35 millimeters in the
minor diameter, and about 30 to 35 millimeters in height. The surface
area of such a solid pest control unit is about 4,000 to 7,000 mm2
and wherein the mass of the solid pest control means is about 3 to 45 or
about 0.2 to 100 grams. The unit can include a buoyancy agent (about 0.1
to 20 wt. %) that can regulate the specific gravity to a desired level
from about 0.85 to about 1.15 depending on the needs of the user. The
materials are then dispersed into gypsum slurry that is poured into
briquette molds, or made into granules or pellets of various sizes, to
form a solid, sinking, pest control composition. Once applied in aquatic
field sites, the surface of the matrix slowly dissolves, releasing many
minute buoyant pesticide laden particles to the water surface over the
life of the product. Once at the surface, the particulate microbial
pesticide release from the buoyant particles and is distributed
throughout the water column to be ingested by susceptible immature filter
feeding mosquitoes and pestiferous flies.

[0017]Control personnel will first inspect and evaluate an aquatic site
for pest activity and then can place the pest control unit of the
invention into the environment. The pest control unit of the invention
can either be manually or mechanically distributed into the aquatic site.
The unit of the invention is typically distributed into the aquatic site
at a rate of about 1 to about 50 (units) of the microbial pesticide per
10 square meter of the aquatic site for effective pest control activity.
To obtain optimal control, the pest control unit is typically distributed
over a large portion of the aquatic site; however, the entire site does
not have to be uniformly treated with the individual units. As the units
contact water in the aqueous site, the microbial pesticide is released at
a substantial rate and is distributed by natural effects throughout the
aquatic site.

[0018]The pest control unit must be applied at least once during a
temperate season or during the breeding season to effectively control
insects, however, the unit can be reapplied to an aquatic breeding site
repeatedly during the breeding season, depending on the amount of
microbial pesticide distributed and the lifetime of the unit. The control
unit can be used at a rate of one 44 gram briquette per each, 10 m2,
5 m2 or 1 m2.

Microbial Pesticide

[0019]The term microbial pesticide as employed here is intended to include
any microbial active material used for control of plants, animals or
microorganisms, such as mosquitoes, fungi, algae, snails, weeds,
including in particular microbial insecticides, microbial biocides, and
other microbial materials of economic value for management of terrestrial
and aquatic environments. Microbial pesticides include microbes that are
pathogen to insect pests that include but are not limited to specific
bacterium, fungus and virus materials.

[0020]A great variety of microbial pesticides can be used which are
compatible with the plaster and buoyant particle composition of the
invention. Representative non-limiting examples of the pesticides are: 1)
bacteria in the genera: Agrobacterium, Ampelomyces, Bacillus,
Pseudomonas, and Streptomyces, 2) fungi in the genera Beauveria, Candida,
Coelomyces, Coniothyrium, Fusarium, Gliocladium, Metarhizium,
Paecilomyces, Pythium, Trichoderma, and Verticillium, and 3) viral agents
such as granulosis virus, and nuclear polyhedrosis viral agents.

[0021]Preferred microbial pathogens for use in the invention are those
that have been found effective as pesticides, or biocides, including
bacteria, fungi, and viruses. The literature reports numerous studies on
the relative biological activity of such microbial pathogens. They
include many species of bacteria, such as Bacillus thuringiensis, widely
used in the control of agricultural pests, Bacillus thuringiensis
israelensis, and Bacillus sphericus effective for the control of immature
flies such as mosquitoes (Culicidae), aquatic midges (Chironomidae),
mushroom flies (Sciaridae) etc. Fungal microbials include Lagenidium
gigantium, Coelomyces, etc. Microbial activity of materials such as the
microbial pesticide of the invention is expressed in International Toxic
Units (ITU). The normal range of ITUs applied in the field for insect
control of the invention control is about 1 lb.-acre-1 to 20
lb.-acre-1 or about 2 lb.-acre-1 to 10 lb.-acre-1 of a 200
ITU/mg of unit or at a rate of about 0.1 to 2 gms-m-2 or about 0.2
to 1 gms-m-2 of a 200 ITU/mg of unit.

[0022]Microbial pathogens commercially developed for the control of
insects of public health importance include Bacillus thuringiensis
israelensis (Bti), Bacillus sphericus (Bsph) and Lagenidium gigantium.
Bti introduced commercially in the early 1980's, quickly found commercial
acceptance and is now used worldwide in public health insect control
programs. Its is widely used because of it's commercial availability,
target specificity (i.e. negligible environmental impact), citizen
preference as a larval control material of choice, its relatively low
cost, rapid direct kill of treated stages, and its effectiveness for the
control of most mosquito species. Bti has few disadvantages. They are: 1)
the microbial particles must be uniformly distributed throughout treated
sites to be ingested (i.e. it is effective only when evenly applied in
field sites), and 2) treatments are short lived, thus provide no residual
control of subsequent mosquito egg hatches.

[0023]Bacillus sphericus (Bsph) was introduced commercially in the mid
1990's, for its residual control capability. Applications to underground
sites and to highly organic waters are reported to control for two to
four weeks at high label application rates. Similarly, Bsph has few
disadvantages. They are: 1) like Bti, the requirement that the microbial
particles be uniformly distributed in treated sites, and 2) the residual
control of subsequent mosquito hatches is short in clean water sites.

Buoyant Agent

[0024]Microbial pesticide particles must be released from the water
surface and ingested by filter feeding target organisms to be effective.
Thus, sinking sustained release pesticide compositions must deliver
particulate pesticide particles to the water surface. This invention
employs a buoyant agent to deliver said particles to the water surface.

[0025]Many different types of buoyant agents with a specific gravity of
less than 1.0, about 0.99 to 0.85 may be used in the invention. As not
all such materials are known and new ones may be developed in the future,
I do not wish to be held to a specific type. Specific gravity is a
unitless measure of the density of a material to the density of water at
a defined temperature.

[0026]Of the materials tested, effective buoyant agents include perlite,
and polypropylene powders with and without internal void space, to which
microbial insecticides are attached. Particle sizes useful include those
in the size range of 1 to 10,000 microns. More preferably, particle sizes
in the range of 2 to 2,000 microns may be used. Most preferably, the
particle size range is between 10 to 1,000 microns.

Plaster

[0027]Sjogren (U.S. Pat. No. 4,732,762) teaches that gypsum dissolves in
water and is an effective high density (sinking) slow release matrix for
water soluble pesticides. Kase (U.S. Pat. No. 4,631,857) describes the
use of plaster in combination with cork and the microbial agent Bacillus
thuringiensis israelensis (Bti) to create a floating microbial
composition. This invention reveals for the first time a unique new
sinking microbial pesticide composition that uses gypsum plasters and
cements with a buoyant agent loaded with microbial powders to slowly
release microbial pesticides to the water surface for mosquito and
pestiferous aquatic insect control.

[0028]Dehydration of gypsum (calcium sulfate dehydrate (CaSO4.2H2O) in an
open kettle by direct heating in the range of 390-570° F., will
result in beta-calcium sulfate hemihydrate, CaSO4.).5H2O, commonly called
plaster. Typically, plaster crystals are long, needle-like, irregular in
shape and porous. The shape and porosity of the crystalline particles
results in high water absorbency. The powder, when mixed with water, will
require about 60 parts of water to about 100 parts of plaster to give a
"workable" slurry consistency. Plasters can contain a variety of
additives that provide properties such as wettability, strength,
hardening rate, particle size and low viscosity slurries. Gypsum cement
is a preferred embodiment with higher compressive strengths and slower
rates of dissolution (Sjogren, U.S. Pat. No. 4,732,762).

[0031]The physical properties of low-density polypropylene powder suitable
to use as a buoyant vehicle, include a particle size range of 1 to 10,000
microns, more preferably 5 to 1000 and most preferably 10 to 500 microns.
The common polypropylene density ranges from 0.86 to 0.91 gram/cubic
centimeter. Suitable densities include any density less than 1.0 capable
of being loaded with particulate microbial active ingredient, the
combination of which when soaked in water >24 hours demonstrates a
specific gravity of less than 1.0.

[0032]The composition is prepared by weighing 5 lbs. of the Bti microbial
active ingredient to which is added 17 lbs. of de-ionized water. The Bti
is then mixed thoroughly to prepare a aqueous slurry. Then 7.8 lbs. of
Accurel polypropylene powder is placed in a mixing vessel. The Bti slurry
is then added and the combination blended well with a mixer and a vacuum
is drawn on the mixture to pull the Bti slurry into the polymer void
space. The loaded powder is then dried, and mechanically ground back to
the initial size of the polymer powder.

[0033]Then 50 lbs. of Plaster of Paris is placed into a mixing vessel with
36.2 lbs. of de-ionized water is added. The plaster is mixed thoroughly
with a 1750 rpm mixer for 5 minutes. Then 12.8 lbs. of Bti loaded polymer
powder and 1 lb. of plaster accelerator is added to the slurry and
blended well. The combined slurry is then placed in briquette molds to
shape the final product form, where it sets up into hard units. Once set,
the units are discharged from the molds, dried and packaged.

[0035]The composition is prepared by weighing 5 lbs. of the Bsph microbial
active ingredient to which is added 17 lbs. of de-ionized water. The Bsph
is then mixed thoroughly to prepare an aqueous slurry. Then 7.8 lbs. of
Accurel polypropylene powder is placed in a mixing vessel. The Bsph
slurry is then added and the combination blended well with a mixer and a
vacuum is drawn on the mixture to pull the Bsph slurry into the polymer
void space. The loaded powder is then dried, and mechanically ground back
to the initial size of the polymer powder.

[0036]Then 50 lbs. of Plaster of Paris is placed into a mixing vessel with
36.2 lbs. of deionized water is added. The plaster is mixed thoroughly
with a 1750 rpm mixer for 5 minutes. Then 12.8 lbs. of Bsph loaded
polymer powder and 1 lb. of plaster accelerator is added to the slurry
and blended well. The combined slurry is then placed in briquette molds
to shape the final product form, where it sets up into hard units. Once
set, the units are discharged from the molds, dried and packaged.

[0038]The composition is prepared by weighing 29 lbs. of a Bti microbial
active ingredient liquid concentrate. The Bti liquid concentrate is then
mixed thoroughly with 7.8 lbs. of Propyltex polypropylene powder in a
mixing vessel. The combined slurry is then blended well with a mixer. The
loaded powder is then dried, and mechanically ground back to a <100
micron powder.

[0039]Then 50 lbs. of Plaster of Paris is placed into a mixing vessel with
36.2 lbs. of de-ionized water is added. The plaster is mixed thoroughly
with a 1750 rpm mixer for 5 minutes. Then 12.8 lbs. of Bti loaded polymer
powder and 1 lb. of plaster accelerator is added to the slurry and
blended well. The combined slurry is then placed in briquette molds to
shape the final product form, where it sets up into hard units. Once set,
the units are discharged from the molds, dried and packaged.

[0041]A representative solid, sinking, combined Bti and Bsph sustained
release microbial pesticide composition is made by weighing 4 lbs. of the
microbial pesticide Bsph and 1 lb. of the microbial pesticide Bsph. The
technical powders are then blended, to which is added 17 lbs. of
de-ionized water. The Bsph & Bti are then mixed thoroughly with the water
to prepare an aqueous slurry. Then 7.8 lbs. of Accurel polypropylene
powder is placed in a mixing vessel. The Bsph & Bti slurry is then added
and the combination mixed well with a mixer and a vacuum is drawn on the
mixture to pull the Bsph slurry into the polymer void space. The loaded
powder is then dried, and mechanically ground back to the initial size of
the polypropylene powder.

[0042]Then 50 lbs. of Plaster of Paris and is placed into a mixing vessel
and 37 lbs. of de-ionized water is added. The plaster is mixed thoroughly
with 1750 rpm mixer for 5 minutes. The 12.8 lbs. of Bti & Bsph loaded
polymer powder and 1 lb. of plaster accelerator is then added to the
plaster slurry and blended in. Then the combined slurry is added into
molds in the final form of the product, where it sets up into hard units.
Once set, the units are discharged from the molds, dried and packaged.

Example V

[0043]A 30-40 day controlled release gypsum granule, <6 mesh in size
was made as follows. Gypsum prills were placed in a rotary blender
(alternatively a sand core) in a prilling drum to form a base. The base
particles are then coated with thin slurry of pre-blended high
compressive strength gypsum, causing the granules to drag. Then 5 to 100
micron Accurel® polypropylene powder, pre-loaded with Bti
(alternatively Bsph) microbial powder was slowly added onto the tacky
slurry coated granules. The powder tacks onto the slurry, drying the
surface of the granule particles, until the granules run free. Next, a
second addition of thin gypsum slurry was added and prilled onto the
granules to form a second gypsum layer, then another addition of
microbial loaded polypropylene powder was added and tacked onto the
slurry until it surface moisture was taken up and granule again free
rolls. This process was repeated again and again to build up controlled
release gypsum particles containing the particle mass required for
application by ground or aerial broadcast application equipment to field
mosquito breeding sites. Once applied, in the presence of water the slow
dissolution of the gypsum coating slowly releases buoyant microbial
pathogen loaded particles to the water surface where the microbial
control agents release into the water column to control immature mosquito
and fly pests.

Mosquito Control Field Trials

[0044]Pellet Trials Against Aedes aegypti--Thailand:

[0045]Dr. Mir Mulla, Professor, Department of Entomology, University of
California, Riverside conducted replicated field trials using 5% Bti,
sinking 1/4 inch diameter by 3/16 inch pellets in 200 liter earthen
domestic water storage jars representative of those that breed the Yellow
Fever and Dengue mosquito vector Aedes aegypti in Bang Bua Thong,
Nonthaburi, Thailand. Ten grams of pellets were added per jar in a
randomized block design experiment. Then 25, 3rd instar mosquito
larvae were added per jar at the start of the experiment and at each
interval. Larval survivors were assessed at 48 hours, and pupal skins
were counted one week after addition of larvae. When larval development
slowed and all larvae not pupated and emerged within a week, pupal skins
were counted and removed on two occasions, after one week and again after
2 weeks. Jars were then challenged again with new larvae. FIG. 1, shows
the efficacy of Bti gypsum pellets against successive cohorts of Aedes
aegypti larvae (25 third-instar larvae/jar) in 200 L earthen water
storage jars.

[0046]Dr. Tianyun Su, Consulting Medical Entomologist, Riverside,
California conducted 4.36 square feet, simulated catch basin, microcosms
trials to evaluate the effectiveness of 12 gram and 44 gram sinking slow
release microbial pesticide briquette compositions, containing 7% Bti in
replicated chambers. Rabbit pellets were introduced as larval food, i.e.
15.5 g/tub, every other week. Culex quinquefasciatus and Aedes aegypti,
early 3rd instars, were used in bioassays wherein 25 larvae were
introduced into floating sentinel cages in each replicate on regular
intervals. Results were expressed as percent inhibition of adult
emergence, I.E. %. Fifty percent of the water in tubs was replaced with
fresh tap water monthly to simulate water dilution in natural catch
basins. Residual weight of the briquettes was measured monthly by
retrieving the briquettes and calculating dry weight according to a
previously determined ratio of wet/dry weight.

[0047]The 12 gram briquettes applied at the rate of 1 briquette/tub,
inhibited the emergence of adult Culex quinquefasciatus mosquitoes by
≧85% for 154 days. The 44 gram briquettes applied at the rate of 1
briquette/tub inhibited Culex quinquefasciatus mosquito adult emergence
≧92% for 154 days, at which time the test was terminated with 1 gm
of briquette remaining.

[0048]The small briquettes at an application rate of 1 briquette/tub also
inhibited the emergence of adult Aedes aegypti mosquitoes by ≧82%
for 154 days. The large briquettes at 1 briquette/tub inhibited Aedes
adult emergence ≧93% for 154 days, when the test was terminated.

[0049]FIG. 2 shows the efficacy of the 12 gram version of the briquette at
a rate of 1 briquette per 200 liter jar or tub against Culex q.

Test Methods

[0050]The test procedures for the graphics data shown in the figures are
as follows. Test materials included Bti pellets applied at 5 lb/ac, 227
mg/tub, and two Bti briquette formulations a 12.5 gm per briquette and a
44 gm briquette. Briquettes were applied at a rate of 1 briquette/tub.
The simulated catch basin microcosm habitat environment employed plastic
tubs with a surface area of 4.36 square feet. Water depth averaged 6
inches; water volume was approximately 15 gallons. Tubs were set up out
of sunlight, under representative catch basin environment conditions.
Rabbit pellets were used as larval food at a dose rate of 0.025%
calculated on the initial water content, i.e. 15.5 g/tub, every other
week. Briquettes using the technology of the invention were used as
treatments and were introduced at flooding. Three replicates of each
treatment material were used. Culex spp (quinquefasciatus and
stigmatosoma) and Aedes aegypti, early third instars were used as
bioassay organisms. Floating sentinel cages were used to demonstrate that
the Bti was released at the water surface, i.e. to prevent larval access
to Bti settled out on the bottom of the chambers. Twenty-five larvae were
introduced per sentinel cage. About 1 gram of rabbit pellets was put in
each cage to insure larval access to sufficient food. Cages were set up
weekly for pellets, initially weekly for small briquettes, then every
other week; and initially weekly, then every other week, then monthly for
large briquettes. Results were expressed as IE %, i.e. percent inhibition
of adult emergence. Culex cages were read twice a week until all larvae
died or pupated and adults emerged. Aedes aegypti cages were also read
twice a week; pupae were collected and introduced to a screened cage
without sugar feeding. Exuviae were counted after all pupae died or
emerged. Emerged adults starved to death inside the cage to prevent
escape of this exotic species. Half of the water in the tub microcosms
was replaced with fresh tap water monthly to simulate water dilution in
natural catch basins. The residual weight of the briquettes was measured
monthly by retrieving the briquettes gently, draining them, then weighing
and calculating the dry weight according to a previously determined
wet/dry weight ratio. The water temperature was monitored with a Taylor
Maximum-Minimum Thermometer at bottom of a tub at regular intervals.

[0051]All microcosm tests were conducted under the same conditions,
discussed above. FIG. 1 presents the control efficacy of Bti pellets
against successive cohorts of Aedes aegypti larvae. FIG. 2 shows the 12
gm Bti briquette provided 97% Inhibition of Emergence (I.E.) control of
Culex quinquefasciatus mosquitoes for 123 days and >85% control for
154 days. FIG. 3 shows the 44 gm briquette achieved >93% I.E. of Culex
quinquefasciatus mosquito larvae for 154 days. Similarly, FIG. 4 shows
the 12 gm Bti briquette gave >97% control for 137 days, and 82%
control at 154 days against Aedes aegypti larvae. Finally, FIG. 5
presents the results of the 44 gm briquette which gave >93% I.E. of
Aedes aegypi mosquito larvae for 154 days. FIG. 6, shows the residual
amount of the 12 and 44 gram briquettes remaining over time. Lastly, FIG.
7 shows the water temperature during the test period.

[0052]The above specification, examples and data provide a basis for
understanding and using the invention as is understood at this time.
While many embodiments of the invention can be made, the invention
resides in the claims that follow.